Apparatus for testing and repairing telephone circuits



H. NYQUIST July 8, 1930.

APPARATUS ,FOR TESTING AND REPAIRING TELEPHONE CIRCUITS Fil ed July 20, 1929 2km, aw?! Core INVENTOR BY Eng/ 151:

ATTORNEY Patented July 8, 1930 UNITEDSTATES PATENT OFFICE HARRY NYQUIST, OF MILLIBURN, NEW' JERSEY, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A GORPORATION OF NEW YORK APPARATUS FOR TESTING AN D REPAIRING TELEPHONE CIRCUITS Application filed July 20,

This invention relates to a method and means for preventing inductive interferences from arising in circuits in a group, such, for example, as in a cable.

The arrangements of the invention are particularly advantageous for preventing the occurrence of interferences which might otherwise originate in the cable, or group, itself due to operations which have to be'carrie'd 19 out in the ordinary working on such circuits,

voice circuits are liable to cause serious interference on adjacent carrier circuits.

There are four elementary operations which may be performed on a pair of conductors which may cause interference in adjacent g carrier circuits. These operations are as follows: A conductor may be suddenly grounded when there is a potential difference between the conductor and ground; the conductor may be removed from ground at a time when there is current flowing from the conductor to ground;the conductor carrying current may be suddenly interrupted; or a' severed conductor may tbe connec ed at a time whenthe two portions are 'd fiere p t nt al- I he eas of th abo e l s d p r iens h r is a av i h a steep front originated which isvery rich in nig i req neies- Comput ti n i at h tthe i t r'f rene lue to th se op ion may, unde unfav'era l co iti ns, be a in exees ief any permis ib e int r n n may eenst ute maj r trouble A d n lyitis one of the primary objects of the ar- "r' ng ment f th inv tion to p v e arrangements whereby the above operations and 1929. Serial No. 379,843.

others may be carried out without causing interference in adjacent circuits. Other ob.- jects and features of the invention will appear more fully from the detailed description thereof hereinafter given.

The invention may be more fully understood from the following description together with the accompanying drawing, in Figures 1 and 2 of which the invention is illustrated. Fig. 1 shows a method of preparing a pair of cable conductors for repair or test work; Fig. 2 shows the method and apparatus of this invention whereby connections may be made to a pair of cable conductors for repair or test purposes without causing any interference in adjacent circuits. Similar reference characters have been utilized to denote like parts in both of the figures.

In Fig. 1 is shown a section of cable 1. Included in the cable would be a group of conductors of which the pair of conductors 4 and 5 are shown. The clamps 6 and 7 are affixed to these conductors and are connected by the strap 8 to clamps, such as 3, whereby a ground connection may be established on the cable sheath 2. Under these conditions no interference will be caused from touching the two conductors together, or to ground, or to testing apparatus, or from cutting them at the points marked XX. However, the establishment of the above described connections,

' or the connection and removal of the clamps,

are just the operations, heretofore pointed out, which will cause inductive interference on adjracent circuits.

In *ig. 2 are shown the arrangements of this invention whereby the above type of connection may be established without suchoperations causing interference on adjacent circuits, In this arrangement are shown the two conductors 4: and 5 with the clamps 6 and 7 aflixed thereto. Each of these clamps is associated with the four-position switches 14 and 21. Switch l t has four positions, position 15 being open, position 16 being connect.- ed to circuit 11 through an inductance 19, p.0-

'sition 17 being directly connected to a circuit 11, and position 18 being connected to circuit 11 through acondenser 20. Switch 21 has four positions, position 22 being open, posi tion 28 being connected to circuit 11 through an inductance 30, position 24 being directly connected to circuit 11, and position 26 being connected to circuit 11 through a condenser 25. Circuit 11 may be completed by means of a switch 10 which is also connected to a clamp 3 which may be grounded on the cable sheath as heretofore. If desired the circuit ll might be completed through a telephone set 12 or a testing set 13.

The procedure with the arrangements of this invention is to connect the clamps 6' and 7 to the conductors 4 and 5 while switches 14 and 21 are 011 theopen positions 15 and 22, respectively. Switch 10, which is connected to clamp 3 grounded on the cable sheath, may then be closed. The next operation is to throw the switches 14 and 21 to the positions 16 and 23 which are connected to circuit 11 1 through the inductances 19 and 30.

these conditions any potential difierence which may exist between the conductors 4 and 5 themselves on the one hand and between the conductors and the cable sheath is equalized, but due to the inclusion of the inductances 19 and in the connection, the process of equalization is not rapidenough to cause appreciable inductive interference in. adjacent circuits. The next operation involves throwing the switches 14 and 21 to the positions 17 and24 whereby the conductors are connected "directly to circuit 11 and to ground. For this operation it is necessary that the'switch be of a make-before-break type. As the conductors Fig; 2 is again connected to the conductors with the switches 14 and 21 on the positions 17 and 24 which are directly connected to circuit .11. The switch 10 is closed. After that the switches 14 and 21 are moved to positions 18 and, 26, respectively, which are connected to circuit 11 through the condensers 20 and 25.

.Thisis again a make-beforebreal: operation. After the operation, anycurrent which flowed previously is interrupted but the interruption is brought about gradually by the condenser becomingcharged so that there is no sudden interruption otthe current. This operation will accordingly cause no interference. After .the' current has reached zero the switches are put in the open position and the clamps maybe removed. a

- Y Thev application tothelconductors of apparatus other than for repair or splicing op- Under erations, such as telephone or testing sets, is

cedure of'operation would be the same as heretofore described except that switch 10 would be left open. 7

lVhile the switches 14 and 21 are shown with only four positions, it might be advantageous to utilize a greater number of positions and to utilize intermediate reactancesteps. In that case the operation of switch 21, for example, would be from the open position 22 to the position connected to the largerinductance; from that position to one connected to a smaller inductance; and finally to the position 24. The operation for opening would be to go from position 24 to a position connected to a large capacity, thence to one connected. to a smaller capacity, and thence to the open position 22.

While the invention has been disclosed as embodied in certain specific arrangements which are deemed desirable, it is understood that it is capable of embodiment in many and 9 other widely varied forms without departing from the spirit of the invention as defined by the appended claims.

- What is claimed is:

1. The method of preventing inductive interference from being caused in circuits in a group by the disconnection from a pair in such group of apparatus utilized for preparing such. pair. for testing or repair purposes, which comprises disconnecting such apparatus from the conductors of said pair gradu- V ally through a capacity.

2. The method of preventing inductive interference from being caused in circuits in a groupby connection and disconnection from a pair in such groupof apparatus forpreparing such pair for testing or repair purposes, which comprises connecting such apparatus to the conductors of a pair through an inductance, eliminating. such inductance from the connection, and disconnecting such apparatus from the conductors of the pair gradually through a capacity.

3. The method of preventing inductive interference from being caused in circuits in a group by the connection to a pair in such group of apparatusfor preparing such pair for testing or repair purposes, which comprises. grounding such apparatus, connecting such grounded apparatus tothe conductors of apair through an inductance, and eliminating the inductance from such connection.

' 4. -A pair of conductors, clamping members "QOlIllQClZlblB to said conductors, a circuit connected to said clamping members, means for liiU grounding said circuit, an inductance, and switching means for completing said circuit through said inductance.

5. A pair of conductors, clamping members connectible to said conductors, a circuit connected to said clamping members, means for grounding said circuit, a capacity, and switching means for including said capacity in said circuit.

6. A pair of conductors, clamping members connectible to said conductors, a circuit associated with said clamping members, means for grounding said circuit, and switching means whereby said circuit may be completed between said clamping members either directly, or through an inductance, or through a capacity.

In testimony whereof, I have signed my name to this specification this 16th day of Jul 1929.

HARRY N Y QUIST. 

